Acrylic polymers are well known for their clarity, sparkling color, surface gloss and weather resistance. Acrylic polymers are also useful as binders, such as in paints and coatings, and cementious compositions.
Acrylic polymers are often supplied in a particulate form for ease of shipping and handling, in the form of beads, granules, or pellets. The acrylic particles can he formed into useful articles by thermal processing—such as by extrusion, injection molding, blow-molding, and other similar processes.
Acrylic powders can also be applied directly to substrates—as in an electrostatic application of fine acrylic particles to a metallic part, followed by heating to fuse the particles into a smooth protective coating.
Acrylic powders can be used in a rotomolding operation, as described in US 2009-224421, in which the powder is rotated within a hot mold, melting, coating and fusing the inside of the mold to form a smooth coating.
Acrylics have been combined with particulate fillers to form a textured surface, such as when metal flakes or granite-look crosslinked particles are extruded with an acrylic polymer powder or pellets to form a spa surface, as described in US 20090093568. The surface may be capped with a thin layer of coextruded acrylic polymer to protect the metal particles from weathering and create a less rough surface.
US 2010-0143629 describes the combination of an acrylic polymer and cross-linked thermoplastic particles to provide a rough texture and matte surface.
U.S. Pat. No. 6,878,780 describes acrylic thermosetting powder coatings that contain pendant functionalities or groups capable of reacting with a dicarboxylic acid. The reaction of the pendant groups and the dicarboxylic acid cross-links or cures the powder coating after application to a substrate. Similarly, acrylic powder resins containing some epoxy functionality are used to form coatings on substrates in U.S. Pat. No. 6,509,420.
Particulate fillers and polymeric powders can be combined and used to form anti-skid transportation surfaces and marking systems, Pavement marking systems currently in use include a topcoat containing particulate fillers selected from the group consisting of reflective elements, skid-resistant particles, magnetizable particles and mixtures thereof. This topcoat is applied as solvent-borne and water-borne paints, preformed adhesive tapes, preformed thermoplastic tapes, two-part reactive thermoset systems, hopper-borne molten thermoplastic systems, and combustion flame-sprayed thermoplastic powder systems. The top-layer having embedded particulate fillers can be further treated with a binder that improves the adhesion between the particulate fillers and the top layer. U.S. Pat. No. 6,180,228 describes a sprayed flame thermoplastic system, where a polymeric powder melted and combined with particulate fillers. This molten admixture is applied to a transportation surface.
US 2008/0115444 describes asphalt roofing shingles with enhanced granule adhesion. A powdered adherent material is added between the protective granules, then melted and fused together to further bind the protective granules and reduce dislodgement by rain, hail, and U.V. deterioration of the substrate. The adherent material preferably comprises a polymeric powder. The preferred adherent material is a high-density polyethylene. The reference does not describe any specific properties of the adherent material, such as glass transition temperature or molecular weights.
There is a need for a system of combining particulate filler and acrylic binders to a substrate, in which the acrylic binder is applied in the form of polymer powder, rather than as a melt—which is hot, or in the form of a solution or latex—which require evaporation.
Surprisingly, it has now been found that acrylic polymer powder of certain composition, molecular weight and particle size can be admixed with particular filler on a substrate, the acrylic polymer then being melted-in-place to form a continuous or non-continuous coating that serves to bind the particulate filler to the substrate, This process allows for easy clean up of extra filler and/or binder as solid particles, and eliminates the need for solvents or evaporation.